Question

How would I add a line to the main function to sort the people vector by Age using the STL sort function?

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;

struct Person
{
    string name;
    int age;
    string favoriteColor;
};

bool sortByName(Person &lhs, Person &rhs) 
{ 
    return lhs.name < rhs.name; 
}

bool sortByAge(Person &lhs, Person &rhs) 
{ 
   return lhs.age < rhs.age; 
}

bool sortByColor(Person &lhs, Person &rhs)
{ 
    return lhs.favoriteColor < rhs.favoriteColor; 
}

int main()
{
    vector<Person> people(5);
    for (int i = 0; i< 5; i++)
    {
        cout << "Person #" << i + 1 << " name: ";
        cin >> people[i].name;
        cout << "Person #" << i + 1 << " age: ";
        cin >> people[i].age;
        cout << "Person #" << i + 1 << " favorite color: ";
        cin >> people[i].favoriteColor;
    }
    //call STL sort function here!
}

Answer 1

**To sort a vector array using STL sort function with our own function then this line of statement is to used.

std::sort(vector_name.begin(), vector_name.end(), compareByLength);

*For sort your data using length the statement will be:

std::sort(people.begin(), people.end(), sortByAge);

*Added some small piece of code to your code to enter a choice and sort based on it:

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;

struct Person
{
string name;
int age;
string favoriteColor;
};

bool sortByName(Person &lhs, Person &rhs)
{
return lhs.name < rhs.name;
}

bool sortByAge(Person &lhs, Person &rhs)
{
return lhs.age < rhs.age;
}

bool sortByColor(Person &lhs, Person &rhs)
{
return lhs.favoriteColor < rhs.favoriteColor;
}

int main()
{
vector<Person> people(5);
for (int i = 0; i< 5; i++)
{
cout << "Person #" << i + 1 << " name: ";
cin >> people[i].name;
cout << "Person #" << i + 1 << " age: ";
cin >> people[i].age;
cout << "Person #" << i + 1 << " favorite color: ";
cin >> people[i].favoriteColor;
}
int choice;
cout<<"Enter your choice to sort.."<<endl;
cout<<"1.By Name 2.By Age 3.Color"<<endl;
cin>>choice;
if(choice==1)
{
cout<<"Sorting by Name"<<endl;
std::sort(people.begin(), people.end(), sortByName);
}
else if(choice==2)
{
cout<<"Sorting by Age"<<endl;
std::sort(people.begin(), people.end(), sortByAge);
}
else
{
cout<<"Sorting by Color"<<endl;
std::sort(people.begin(), people.end(), sortByColor);
}
for (int i = 0; i< 5; i++)
{
cout << people[i].name<<" ";
cout << people[i].age<<" ";
cout << people[i].favoriteColor<<" ";
cout<<endl;
}
}